Field of Invention
This generally relates to three-dimensional joint motion evaluation using computer-controlled torque application via, for example, a robotic knee testing device (an “RKT” device) which controls the direction, rate, and magnitude of forces applied in at least three directions. The respective forces are configured to evaluate “IE” (internal-external) movement about a Z-axis of rotation distal to the foot, varus-valgus conditions about a Y-axis of rotation distal to the foot, and “AP” (anterior-posterior) movement of the tibia through a proximal tibia contact arm which rotates about a X-axis of rotation distal to the foot.
Description of Related Art
The knee is composed of the femur or thigh bone, the tibia or shin bone and the patella or knee cap. They are connected by fibrous structures called ligaments which allow a certain amount of ‘joint play’ or motion to exist between the bone structures. When this ‘joint play’ is increased or decreased, an abnormal or pathological condition exists in the knee. Attempts have been made in the past to quantify this increase or decrease in ‘joint play’ of the knee with limited success.
An injury to the knee can cause damage to one or more of the structures of the knee causing an increase in the ‘joint play’ or motion of the knee. This increase in ‘joint play’ can create the sensation to the patient that the knee is slipping or ‘coming out of joint’. Commonly, this sensation described by the patient is referred to as the feeling of ‘joint instability’. The ability of the two bones to actually ‘come out of joint’ is related to the length of the fibrous structures or ligaments which connect the two bones together as well as the shape and size of the two bones (or three). The ability of the bones to ‘come out of joint’ or become unstable is related to the amount of stretch or the amount of increased lengthening of each ligament, the number of ligaments involved, and damage to other support structures of the knee such as the bone itself and the menisci. Accurate measurement of this increased ligament length can be critical to restore the knee to as close to its original functional and anatomical state as possible.
Currently, there are only manual tests used by clinicians to aid in the diagnosis of ligament damage resulting in a change in joint play. As an example, there are three manual tests to evaluate the increased joint play associated with an ACL tear—the Lachman's test, the Pivot Shift test and the Anterior Drawer Test. All of these tests suffer from the clinician's subjective evaluation of both the extent of the ligament lengthening and the change in the compliance or stretchiness of the ligament.
The Lachman's test is performed by laying the patient in a supine position and bending the knee at approximately 20 to 30 degrees. The clinician places a hand on the patient's upper thigh and his other hand below the upper part of the patient's calf. Pressure is applied under the patient's calf and down on the patient's thigh such that there is a translation between the femur and the tibia.
Similar to the Lachman's test, the pivot shift test begins by positioning the patient on his back. The knee is placed in full extension (x-axis rotation) and a valgus (y-axis rotation) force and an internal rotation (z-axis rotation) force is applied to the knee to allow the lateral tibia to slip anteriorly from underneath the lateral femoral condyle as the knee is flexed (x-rotation) the tibia is allowed to slip suddenly back underneath the femoral condyle. The clinician feels for an abnormal external rotation (z-axis rotation) and posterior translation (y-axis translation) of the tibia with respect to the femur. This shift is felt to represent the relative increased translation (y-axis translation) of the lateral side of the knee with respect to the increased translation (y-axis translation) of the medial side of the knee. Furthermore, the point of sudden shift represents the point at which the tibia bone slides from in front of the radius of curvature of the curved end of the femur back to its normal position under the femoral condyle. The clinician subjectively rates the pivot shift as Grade I, Grade II or Grade III depending upon the degree of rotational and translational shift felt during the test. This test is difficult to perform, difficult to teach and difficult to quantify.
Finally, the anterior drawer test is performed with the patient lying on his back and his knee bent 90 degrees. With the patient's foot supported by a table or chair, the clinician applies pressure to the knee using her thumbs. This test is graded based on the amount or extent of anterior translation of the tibia with respect to the femur. Grade I has 0 to 5 mm of anterior translation Grade II has 6 to 10 mm of anterior translation, and Grade III has 11 to 15 mm of anterior translation.
To diagnose an injured ACL using the described tests, the clinician must determine whether the knee feels “abnormal.” Thus, the accuracy of an ACL injury diagnosis using currently known tests depends on the skill and experience of the clinician. A misdiagnosis can lead to unnecessary delay in treatment, thereby placing the patient at increased risk for further damage to the knee.
There are manual tests for the LCL, MCL and the PCL. Each manual test relies on grading the ligament lengthening based upon relative increase in joint play into three categories. There is no effort to grade the compliance of the ligament; however, the expert clinician will describe the ligament in terms of its ‘feel’. The more ligaments and structures that are damaged; the more complex it becomes to perform a manual knee examination with accuracy.
There have been multiple attempts in the past to instrument the knee and quantify or measure the change in the structure of the knee after ligament damage. Several devices have attempted to accurately quantify the extent or relative displacement and compliance of a ligament in the knee. One of these devices is The KT-1000 and the KT-2000 Medmetric®, which measures the anterior-posterior translation of the tibia with respect to the femur along the y-axis, but disadvantageously attach to the tibia. These devices attempt to quantify the findings found when the clinician uses the Lachman's test and the Anterior Drawer Test. Force is applied to a handle on the device which measures force and signals to the clinician the amount of force with a low pitched sound for a 15 pound force and a higher pitched sound for a 20 pound force. This force pulls anteriorly along the y-axis through a strap that wraps underneath the calf. The measurement of the translation uses a technique measuring the relative motion of a pad on the anterior tibia with respect to a pad placed on the patella. This device does not measure relative displacement or compliance in any of the other degrees of freedom previously described in the knee. Furthermore, the quantified results of the KT-1000 or KT-2000 have not been correlated with patient satisfaction whereas the subjective Pivot Shift test has been correlated with patient satisfaction. Other devices such as the Stryker KLT, the Rolimeter, and the KSS system use similar mechanisms to attempt to quantify the normal amount of ‘joint play’ or motion between the femur and tibia, along with any increased ‘joint play’ or motion which is associated with ligament lengthening and damage.
Many non-invasive systems utilize sensors or markers that are attached to the skin, including but not limited to optoelectronic, ultrasonic, and electromagnetic motion analysis systems. These skin sensors or markers are merely representations of location of the underlying bones; however, many published reports have documented the measurement error related to skin artifact with this system. In order to avoid the inaccuracies associated with skin artifact, medical imaging systems may be utilized in order to precisely determine the position/location of the bones accurately.
Surgeons manually examine the joint for altered play; however, due to the variability in size of the patient, size and experience of the surgeon, and the subtlety of injury, consistent and reproducible reports of joint play between surgeons is not possible. The need that must be met is to provide a controlled application of torque during joint examination, with the magnitude, direction, and rate of torque application being controlled. Many reports have documented that, whether performed by hand or with manual arthrometers, the manual application of torque varies between clinicians, thus creating inconsistencies in the examination of joint play.
Accordingly, there is a need for an accurate, objective, reliable and reproducible measure of the impact of damage to the ACL as well as other ligaments and structures in the knee or combination of ligaments and other structures in the knee that can be used in the clinical setting on patients. For example, since an injury to the ACL produces both an increase in anterior translation (y-axis translation) and rotation (z-axis rotation), an objective measure of these changes would both aid in the diagnosis of the injury as well as verify its restoration after ligament reconstruction surgery. Additionally, measurement of displacement and compliance around different degrees of freedom in the knee would help objectively describe the individual and complex changes to ‘joint play’ that occurs in an injured knee with structural damage. A need exists for systems and methods that can provide accurate, reproducible and objective data on the changes in ‘joint play’ or motion that occurs with an injured knee compared to their healthy knee and to the population as a whole such that the clinician can achieve patient satisfaction with focused, biomechanical and proven surgical interventions specific to that injury and for that knee across the entire population of damaged knees.
Needs also exist for systems and methods, and devices which accommodate variances of patient body structure; it may well be understood that each human body is different and may require particular attention when being treated and/or analyzed; this may be particularly evident in the case of abnormalities of bones, tendons, joints, etc., due to injury or the like. Needs also exists for systems and methods, and devices that can provide the type of accurate, reproducible and objective data described above without inherently and/or indirectly adversely impacting the accuracy, reproducibility, and/or objectiveness of the tests and measured data therein.